The field of art of this invention is the one encompassing processes in which a hydrogen rich gas is produced by a chemical reaction between water in any state and a metal or metallic compound. The field is further defined in that the metal or metallic compound which is consumed (i.e. oxidized) in the above reaction is regenerated by reaction with a carbonaceous reducing gas. Thus the metal or metallic compound is an intermediate, not being consumed in the process. Also included are those processes which form either hydrogen or a reducing gas by reacting a carbonaceous feedstock such as light hydrocarbons with steam in a reformer.
Typical prior art related to this field of invention is described in U.S. Pats. Nos. 3,539,292, 3,821,362, and 3,441,393.
Some of the problems existing in the prior art practice of this field of invention are as follows.
Heretofore, processes using intermediate oxidation reduction to produce hydrogen rich gas, such as the steam iron process, have used a simple air blown partial combustion furnace to generate the required reducing gas. This capability of converting a reducing gas with high nitrogen content into high purity hydrogen has been considered the main advantage of the intermediate oxidation-reduction type of process, as it eliminates the need for either expensive pure oxygen, or for expensive steam reformers which can only use gaseous hydrocarbons or naphtha as feedstock. However two disadvantages have attended the intermediate oxidation reduction processes. First, there is always a considerable quantity of both chemical and thermal energy energy left in the exhaust reducing gas. Secondly, when the nitrogen content of the reducing gas becomes large, several penalties accrue: in elevated pressure systems, compression costs go up; additional losses of thermal energy occur due to heating the extra nitrogen, and process equipment has to be sized larger. Thus it can be seen that the intermediate oxidation reduction type of process would yield improved results if the energy of the exhaust reducing gas could be converted into additional reducing gas and if the nitrogen content of the reducing gas could be decreased.
Conventional steam reforming processes for production of hydrogen rich gas involve a complex train of high technology, high cost equipment: a large catalytic primary reformer, one or two catalytic shift converters, a CO.sub.2 removal system, and a catalytic methanator. The efficiency of converting fuel to hydrogen in these processes is generally less than 65%, owing to the following problems: large amounts of heat must be supplied to the primary reformer at temperatures greater than 1150.degree. K., creating substantial amounts of high temperature exhaust gas. Approximately three times as much steam as the stoichiometric requirement must be fed to the reformer in order to achieve desired equilibrium conditions, i.e. reasonably complete conversion of the hydrocarbon, thereby adding substantially to the heat load. The energy released by the exothermic shift reaction is at such a low temperature that little can be recovered in useful form.
Thus the steam reforming processes could yield improved results if it were possible to decrease the proportion of steam fed to the primary reformer, decrease the necessary degree of hydrocarbon conversion and heat load of the primary reformer (given that the same amount of reducing gas is generated), and eliminate or decrease the size of the various purification units.
By combining the most advantageous features of both the steam reforming process and the intermediate oxidation reduction process, it has been discovered that all of the above mentioned improvements can be achieved.
Other problems existing in the prior art are that appreciable quantities of ammonia synthesis gas which are dissolved in high pressure liquid ammonia and which come out of solution when the pressure is decreased are either vented or merely used as process fuel, thereby not efficiently recovering their energy content.